In seeking higher areal recording densities on rigid magnetic disk surfaces, it is known that thin film media have significant advantages over particulate disk media. One of these advantages is the extremely smooth surface exhibited by thin film disks. Because the recording density of a magnetic recording disk is inversely proportional to the distance (fly height) between the disk and the transducing head with which the information is being recorded, the surface of the disk should be extremely smooth to permit a low fly height. However, the extreme smoothness of a thin film disk generally results in a high contact area between the disk and head which, in turn, results in a high value of stiction or friction. High stiction is undesirable because it can cause severe damage to the disk and recording head when the head suddenly breaks free from the disk surface, once disk rotation is initiated. Additionally, as the disk begins to rotate, damaging forces are applied tangentially to the head suspension and the disk drive motor.
In order to improve the tribology of the disk, an overcoat, typically carbon, as well as a lubricant are applied to the outermost film layer of the disk. However, extremely smooth disks, even with a lubricant coating, may still exhibit unacceptably high stiction levels. Moreover, over a period of time the lubricant can become dislodged from the disk surface.
One way to overcome the problems of high stiction while promoting retention of the lubricant is to roughen the surface of the substrate, typically a nickel-phosphorous coated aluminum-magnesium disk, prior to the deposition of the magnetic layer. This is customarily done by a mechanical abrasive technique and is known in the magnetic disk industry as texturing. However, mechanical texturing forms weldments and asperities along the texture lines. These weldments can require an increased fly height and cause severe wear of the magnetic layer during operation of the disk. In addition, the surface texturing process is time consuming, costly, difficult to control, and has not been applied successfully to glass, ceramic or amorphous carbon substrates. Therefore, it is desirable to texture or roughen the substrate surface by means other than mechanical abrasion while not adversely affecting the disk's magnetic properties.
U.S Pat. Nos. 5,053,250 and 5,134,038, assigned to the same assignee as the present invention and hereby incorporated by reference, describe a method and structure that eliminates the need for mechanical texturing by applying an underlayer of a transient liquid metal (TLM) film, preferably gallium, indium, tin, or their alloys, between a non-wettable substrate and the magnetic thin film. The transient liquid metal layer is applied while the substrate, which is not wettable by the liquid metal, is maintained at a condition at which the initially liquid metal remains in a liquid state, and preferably at a temperature above the melting point of the transient liquid metal. The result is that the liquid metal is caused to "ball-up" and form a layer of disconnected molten metal features.
The substrate is maintained at a temperature above or close to the melting point of the transient liquid metal during sputter deposition of the TLM layer onto the substrate. The outer magnetic layer, which may be a binary, ternary or quaternary cobalt-based alloy, such as CoCr, CoRe, CoPt, CoNi, CoNiCr, CoPtCr, CoPtCrTa, CoNiCrTa, or CoPtCrB, is then deposited onto the transient liquid metal at either an elevated temperature above the melting point of the transient liquid metal or alternatively at a more conventional lower temperature at which the TLM layer features, while undercooled, are nevertheless metastably liquid. The transient liquid metal becomes alloyed with the magnetic layer thereby imparting to the magnetic layer a controlled topology which provides a disk surface with improved tribology. The resulting magnetic medium does not include a pure transient liquid metal underlayer.
However, the above described alloying between the TLM layer and the magnetic layer is often undesirable as it causes degraded magnetic performance. Specifically, the interaction between the TLM layer and the magnetic layer can lower the remanent magnetization and coercivity of the magnetic medium. Therefore, it is often desirable to place an intermediate metal layer between the TLM layer and the magnetic layer. Preferred metal films for the interlayer are chromium, molybdenum, vanadium, palladium, titanium, ruthenium, rhodium, niobium, aluminum and platinum, or alloys of these metals. The advantages of such an interlayer and a method of depositing it are described in U.S. Pat. No. 5,063,120, assigned to the same assignee as the present invention and hereby incorporated by reference. In addition to reducing the interaction between the layers, the interlayer provides improved magnetic performance by aligning the (100) plane of the interlayer parallel to the recording surface. This allows the cobalt alloy atoms of the magnetic layer to attach to the interlayer structure with their C axis parallel to the (100) plane.
Unfortunately, the use of such desirable metal layers between the underlayer and the magnetic layer can lead to difficulties in maintaining the disconnected metal features of the TLM layer. In particular, in-situ deposition (sequential deposition without a vacuum break) of a metal layer on top of a TLM underlayer causes the disconnected molten features of the underlayer to coalesce and form a continuous film, thereby destroying the desirable texturing effect of the transient liquid metal underlayer. A method is needed whereby the desirable interlayer can be deposited without causing the TLM layer to coalesce. Furthermore, the method should be adaptable to in-situ deposition of all the required films. That is, the technique should allow the required films to be deposited in a single deposition apparatus without a need to transfer the magnetic medium between deposition tools. In-situ deposition is preferable because it reduces contamination, handling, and process control problems that arise whenever a substrate is transferred between separate sputtering systems.